three schema architecture

1.internal schema

2.conceptual schema

3.External Schema

defines the capture of a database

1.define data storage details, when, what?
- access only to database admin or autherised by admin
2.-access of actual data and the realationship
- access to experienced user
3.-give external view specific to end user

comm b/w external schema and conceptual schema is extenal/conceptual mappint

comm b/w internal schema and conceptual schema is conceptual/internal mappint

data independence

abiliity to change the data at a particular level without affecting the other

ability to change or modify conceptual schemal without affecting external level

eg: data retrival and modify

ability to change or modify internal schemal without affecting conceptual schema

eg: change file structure, add indexing

data definition lang (ddl)

data manipulation lang (dml): - procedural and non procedural dml

to specify conceptual schema

ddl used to define internal and external schemas

some dbms have sotrage definition lang used to define internal and view definition lang to define external

to modify data

can be used with high level lang

dml can alternatively be applied as query directly (called a query lang)

mention the query along with position pointer

only retirve one row at a time

what data to retrive rather than how to retrive it

also called declarative lang